1. Field of the Invention
This invention relates to a semiconductor device manufacturing method, and more particularly to a method of making connection holes, such as contact holes.
2. Description of the Related Art
In a semiconductor device, plugs made of conducting material have been used. Each of the plugs electrically connects a transistor to a wiring layer above the transistor or a lower wiring layer to an upper wiring layer. To do this, a connection hole, such as a contact hole or a via hole, is made in the insulating film covering the transistor or in the insulating film between the lower wiring layer and upper wiring layer and then is filled with conducting material, thereby forming a plug.
For instance, when a contact hole is made, an insulating film is etched using, for example, RIE (Reactive Ion Etching) techniques. In this etching, a damage layer is formed on the sidewall and at the bottom of the contact hole. The damage layer is removed by, for example, a wet process. However, the surface of the conducting layer, such as a metal silicide layer, exposed at the bottom of the contact hole after the damage layer has been removed is non-uniform. Moreover, during the removal of the damage layer, another damage layer and a native oxide film are formed. When a barrier metal is formed in the contact hole with the damage layer and native oxide film being left as described above, the contact resistance increases and the characteristic of the transistor deteriorates. Therefore, it is necessary to remove the damage layer and native oxide film completely.
To remove a damage layer formed in a contact hole, techniques using only dry cleaning have been developed (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-236021).
In the conventional cleaning method, however, it was difficult to sufficiently remove the damage layer and native oxide film in the contact hole. Therefore, a semiconductor device manufacturing method capable of sufficiently removing the damage layer and native oxide film in the contact hole has been desired. Furthermore, when a contact hole is made in a plurality of insulating films stacked one on top of another, steps might develop in the contact hole. Therefore, the development of the technique for removing the steps has been desired.